Bismuth carboxylates as precursors for the incorporation of bismuth in oxide-based materials

The use of bismuth(III) carboxylates (acetate, oxoacetate, lactate, oxalate) as precursors for the incorporation of this element on oxide supports is evaluated as a new tool to generate bismuth-based oxide phases at the surface of MoO3 or WO3 supports. These insoluble precursors are deposited as small particles from a slurry in a liquid hydrocarbon under appropriate experimental conditions, Bismuth molybdate and tungstate phases are produced by solid-state reactions between in situ generated Bi2O3 and the supporting oxide at 673 K. The samples are characterized by specific surface area measurements, X-ray diffractometry, and X-ray photoelectron spectroscopy, The selective oxidation of isobutene to methacrolein is employed as a reaction test to demonstrate the applicability of this approach, The use of precursors containing lactate or acetate-type ligands is found to generate materials displaying enhanced specific surface area and high bismuth-to-molybdenum surface atomic ratios. This bismuth enrichment of the surface is indicative of the presence of dispersed crystallites of either Bi2O3 itself or ternary Bi-Mo-O or Bi-W-O phases, which are known to promote partial oxidation of alkenes, The performances of these materials in the isobutene to methacrolein conversion are indeed in most cases definitely better than those of the so-called reference materials obtained from the simple mixtures of the same oxides prepared separately. (C) 1996 Academic Press, Inc.